(1) Field of the Invention
The invention relates to a method of photolithographic etching of AlCu lines, and more particularly, to a method of photolithographic etching of AlCu lines having excellent critical dimension control and resulting in a tapered profile of the AlCu lines in the manufacture of integrated circuits.
(2) Description of the Prior Art
Due to the limitation of poor etch rate selectivity to photoresist, a thick photoresist mask is often needed during AlCu etching. As a result, the depth of focus in photolithography processes becomes even more challenging. Conventionally, a layer of titanium nitride is deposited over the AlCu layer as a barrier and anti-reflective coating layer (BARC). Conventional etchant gases are BCl.sub.3 and Cl.sub.2. These gases have been found to be insufficient in producing polymer on the sidewalls of the AlCu lines which would prevent undercutting during ethching.
U.S. Pat. No. 4,915,779 assigned to Motorola uses a protective oxide layer over AlCu and etches both the oxide and the AlCu layers under vacuum. U.S. Pat. No. 5,449,639 to Wei et al teaches the use of a disposable titanium nitride anti-reflective coating in etching an underlying metal layer. U.S. Pat. No. 4,412,885 to Wang et al shows a method of etching an Al layer using BCl.sub.3 and Cl.sub.2 with a dopant gas containing oxygen and a fluorocarbon. U.S. Pat. No. 4,511,429 to Mizutani et al teaches dry etching of Al using a hydrogen-containing gas. U.S. Pat. No. 4,919,748 to Bredbenner et al shows a method for tapered etching of metal layers using chlorine and trifluoromethane gases.